Current-limiting fuse having fuse link with longitudinal groove



Nov. 24, 1970 F. J. KOZACKA CURRENT-LIMITING FUSE HAVING FUSE LINK WITH LONGITUDINAL GROOVE Filed April 5, 1969 2 Sheets-Sheet 1 FIG. I

FIG.4

. KOZACKA ATTY.

Du 0 4 m I m K I C I .l. u m m u m m n I W Y e I n B U ,H I u III FIG

Nov. 24, 1970 F. J. KOZACKA 3,543,210

GURRENT-LIMITING FUSE HAVING FUSE LINK WITH LONGITUDINAL GROOVE Filed April 3, 1969 2 Sheets-Sheet 2 INVENTOR:

FREDERECK J. KOZACKA WWW WW ATTY.

United States Patent O 3,543,210 CURRENT-LIMITING FUSE HAVING FUSE LINK WITH LONGITUDINAL GROOVE Frederick J. Kozacka, South Hampton, N.H., assignor to The Chase-Shawmut Company, Newburyport, Mass. Filed Apr. 3, 1969, Ser. No. 813,033 Int. Cl. H01h 85/08 U.S. Cl. 337-159 3 Claims ABSTRACT OF THE DISCLOSURE BACKGROUND OF INVENTION The constituent components of most current-limiting fuses are a tubular casing of insulating material, a pair of terminal elements closing the ends of the casing, a pulverulent arc-quenching filler inside the casing, and a ribbon fuse link of a current-limiting metal inside said casing, submersed in said filler and conductively interconnecting said pair of terminal elements.- The term current-limiting metal is used in this context in a generic sense intended to include, and to be limited to, silver and copper.

US. patent 3,413,586 to Erwin Salzer, issued Nov. 26, 1968 for Electric Current-Limiting Fuse discloses a fuse of the above description. Its ribbon fuse link has transversely extending grooves bounded by regions of progressively increasing cross-sectional area. Such a fuse link lends itself well both to use in fuses having relatively high current ratings and to use in fuses having relatively low current ratings. If the fuse link is relatively thick, the transverse grooves in the fuse link may be established by rolling operations, and the progressive increase of cross-sectional area in the regions bounding the transverse grooves may be achieved by punching or blanking operations. If the fuse link is critically thin the link is preferably supported by a substratum of insulating material integral with the fuse link in which case the desired shape may be imparted to the fuse link by chemical machining.

Considering a relatively thick fuse link whose grooves are established by a rolling operation, such a rolling operation increases the length of the fuse link on account of displacement of metal in a direction longitudinally of the fuse link at points where transverse grooves are being rolled into it. As will be shown below more in detail, a ribbon fuse link configuration predicated upon a groove extending in a direction longitudinally of the fuse link is preferable to the presence of one having transverse grooves.

SUMMARY OF INVENTION In an electric fuse including a tubular casing of insulating material, a pair of terminal elements closing the ends of the casing, a pulverulent arc-quenching filler inside the casing, and a ribbon fuse link of a current-limiting metal inside the casing, submersed in said filler and conductively interconnecting the pair of'terminal elements the fuse link defines a groove extending in a direction longitudinally of the link establishing a longitudinally extending region of reduced cross-sectional area laterally bounded by a pair of regions of relatively large crosssectional area, said regions of relatively large cross-sectional area being interrupted by pairs of juxtaposed cutouts each to both sides of said groove, extending at least to the lateral walls of said groove and defining points of minimal cross-sectional area coextensive with the bottom of said groove and spaced in a direction longitudinally of said fuse link.

BRIEF DESCRIPTION OF DRAWINGS FIG. 1 is an isometric view of a portion of a strip or blank of silver or copper for making a fuse link according to this invention;

FIG. 2 is an isometric view of the strip or blank of FIG. 1 upon having been provided with a groove extending in a direction longitudinally thereof;

FIG. 3 shows the structure of FIG. 2 upon having undergone a blanking or punching operation;

FIG. 4 is a section along IVIV of FIG. 5 and shows a complete fuse embodying this invention;

FIG. 5 is a section along V-V of FIG. 4;

FIG. 6 is a section along VI-VI of FIG. 5;

FIG. 7 is an isometric view of a blank similar to that shown in FIG. 2 but including portions of silver and portions of copper; and

FIG. 8 is an isometric view of a fuse link similar to that shown in FIG. 3 but including portions of silver and portions of copper.

DESCRIPTION OF PREFERRED EMBODIMENT OF THE INVENTION Referring now to the drawings, and particularly to FIGS. 1-3, when a groove 2 is being rolled into a blank 1, the width W of the blank increases to W, i.e, W W, and the thickness of the blank is decreased along groove 2. Provision of groove 2 has no effect upon the length of blank or strip 1. Grooved strip 1 is then subjected to a blanking operation, as a result of which it assumes the shape of FIG. 3. The structure of FIG. 3 has a pair of juxtaposed substantially V-shaped cut-outs 3 arranged to both sides of groove 2. Each of said pair of cut-outs 3 has a closed end 4 and an open end 5. Open ends 5 are coextensive with one of the lateral edges 1a of blank or ribbon fuse link 1. The closed ends 4 of the aforementioned cut-outs are preferably coextensive with the lateral walls 2a of blank or fuse link 1 and coextensive, with the bottom of groove 2. If desired cut-outs 3' may extend into the bottom groove 2. The portion M of the bottom of groove 2 situated between cut-outs 3 is a point of minimum cross-sectional area.

Referring now to FIGS. 4-6, tubular casing 6 of insulating material is closed on both ends thereof by terminal elements 7 in the form of caps mounted on casing 6. The inside of easing 6 is filled with a pulverulent arcquenching filler 8, preferably quartz sand. Ribbon fuse link 1 of copper or silver is arranged inside of casing 1, submersed in filler 8 and conductively interconnects terminal caps 7. To this end, terminal caps 7 are provided with slits for the passage of ribbon fuse link 1 and define recesses for receiving solder joints 9 conductively connecting link 1 and caps 7. Fuse link 1 has the same geometry as that shown in FIG. 3, except that the number of pairs of juxtaposed cut-outs 3 is larger than one. As shown in FIGS. 4 and 5, the number of juxtaposed pairs of substantially V-shaped cut-outs is seven. Groove 2 extends continuously along the entire length of fuse link 1.

Where it is necessary, or desirable, to cut the cost of materials, fuse link 1 may be made of silver and copper similarly as shown in US. Pat. 2,809,257 to K. W. Swain, issued Oct. 8, 1957 for Composite Fuse Links of Silver and Copper. The structure shown in FIG. 2 may also be obtained by bonding, e.g. rolling to a strip of silver having substantially the width W two spaced strips of copper, the spacing between these strips of copper establishing the groove 2 of FIG. 2. A composite fuse link of silver and copper according to this invention thus includes a bottom portion of the groove 2 being of silver only, and regions of relatively large cross-sectional area wherein copper may be superimposed upon a layer of silver, but which are preponderantly of copper. FIG. 7 is an isometric view of a blank including a lower layer of silver and an upper layer of copper as described above and FIG. 8 is an isometric view of a fuse link derived from the blank of FIG. 7 by appropriate blanking or stamping operations. The structure of FIG. 8 bears the same relation to that of FIG. 7 as the structure of FIG. 3 to that of FIG. 2. The same reference characters have been applied in FIGS. 7 and 8 as in FIGS. 1 and 2 to designate like parts. In FIGS. 7 and 8 the symbol Cu has been applied to designate portions made of copper and the symbol Ag has been applied to designate portions made of silver.

Considering two ribbon fuse links having both the same current rating of which one conforms substantially to FIG. 1 of the aforementioned U.S. Pat. 3,413,586, and the other conforms substantially to the fuse link shown in FIGS. 4 and of the instant drawings and embodying the present invention, both fuse links being formed by rolling and subsequent punching or blanking, it will be apparent that their width and their length differ significantly. Rolling of transverse grooves into a metal ribbon such as that shown in FIG. 1 tends to increase the length of the ribbon without significantly affecting the Width thereof. Rolling a groove into a metal ribbon in a direction longitudinally thereof such as shown in FIG. 2 tends to increase the width of the ribbon without significantly affecting the length thereof. As a result, fuses having fuse links according to the present invention tend to have a larger number of necks or break-forming points of minimum cross-sectional area per unit of link length. This means that such fuses tend to generate a relatively higher aIc voltage and, therefore, tend to minmize arcing i -t values. The fact that the width W of the ribbon fuse link is slightly increased in comparison to the width W of the blank or ribbon has hardly any effect upon the operation of a fuse embodying this invention.

I claim as my invention:

1. An electric fuse including a tubular casing of insulating material, a pair of terminal elements closing the ends of said casing, a pulverulent arc-quenching filler inside said casing, and a ribbon fuse link of a current-limiting metal inside said casing, submersed in said filler and conductively interconnecting said pair of terminal elements wherein the improvement consists in that said ribbon fuse link is provided with a groove extending in a direction longitudinally of said ribbon fuse link establishing a longitudinally extending region of reduced crosssectional area laterally bounded by a pair of regions of relatively large cross-sectional area, said regions of relatively large cross-sectional area being interrupted by pairs of juxtposed cut-outs, each cut-out of said pairs of cutouts being arranged to opposite sides of said groove and extending at least to the lateral walls of said groove and defining points of minimum cross-sectional area coextensive with the bottom of said groove and spaced in a direction longitudinally of said fuse link.

2. An electric fuse as specified in claim 1 having a ribbon fuse link wherein pairs of juxtaposed substantially V-shaped cut-outs are arranged to both sides of said groove, each of said pairs of cut-outs having a pair of closed ends coextensive with the bottom of said groove and a pair of open ends each coextensive with one of the lateral edges of said fuse link.

3. An electric fuse as specified in claim 1 wherein said fuse link includes silver and copper, the bottom portion of said groove along its entire length being of silver only and said regions of relatively large cross-sectional area being preponderantly of copper.

References Cited UNITED STATES PATENTS 3,413,586 11/1968 Salzer 337159 2,809,257 10/1957 Swain 337-159 BERNARD A. GILHEANY, Primary Examiner D. M. MORGAN, Assistant Examiner U.S. Cl. X.R. 

